Jackie-Jiang commented on code in PR #16727:
URL: https://github.com/apache/pinot/pull/16727#discussion_r2356677290
##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/recordtransformer/DataTypeTransformer.java:
##########
@@ -128,6 +89,62 @@ public void transform(GenericRow record) {
}
}
+ /**
+ * Convert a single value to the target PinotDataType.
+ * This method can be reused by other components that need single value
conversion.
+ *
+ * @param value The value to convert
+ * @param dest The target PinotDataType
+ * @param columnName The column name (for error reporting)
+ * @return The converted value
+ */
+ public static Object convertValue(@Nullable Object value, PinotDataType
dest, String columnName) {
Review Comment:
(minor) `value` is never `null` (caller ensures that). Let's remove the
`@Nullable` and null check. The return value could actually be `null`, so let's
annotate the return value as `@Nullable`. Also suggest renaming `dest` to
`targetType`
```suggestion
@Nullable
public static Object convertValue(Object value, PinotDataType targetType,
String columnName) {
```
##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/readers/PinotSegmentColumnReaderImpl.java:
##########
@@ -0,0 +1,146 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.segment.local.segment.readers;
+
+import java.io.IOException;
+import javax.annotation.Nullable;
+import org.apache.pinot.common.utils.PinotDataType;
+import org.apache.pinot.segment.local.recordtransformer.DataTypeTransformer;
+import org.apache.pinot.segment.spi.IndexSegment;
+import org.apache.pinot.spi.data.FieldSpec;
+import org.apache.pinot.spi.data.readers.ColumnReader;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * Implementation of ColumnReader for Pinot segments.
+ *
+ * <p>This class wraps the existing PinotSegmentColumnReader and provides the
ColumnReader interface
+ * for columnar segment building. It handles:
+ * <ul>
+ * <li>Reading column values from Pinot segments</li>
+ * <li>Data type conversions when target schema differs from source</li>
+ * <li>Null value detection</li>
+ * <li>Resource cleanup</li>
+ * </ul>
+ */
+public class PinotSegmentColumnReaderImpl implements ColumnReader {
+ private static final Logger LOGGER =
LoggerFactory.getLogger(PinotSegmentColumnReaderImpl.class);
+
+ private final PinotSegmentColumnReader _segmentColumnReader;
+ private final String _columnName;
+ private final int _numDocs;
+ private final boolean _needsConversion;
+ private final FieldSpec _targetFieldSpec;
+
+ private int _currentIndex;
+ private Object _currentValue;
+ private boolean _currentIsNull;
+
+ /**
+ * Create a PinotSegmentColumnReaderImpl for an existing column in the
segment.
+ *
+ * @param indexSegment Source segment to read from
+ * @param columnName Name of the column
+ * @param targetFieldSpec Target field specification (may differ from source
for data type conversion)
+ */
+ public PinotSegmentColumnReaderImpl(IndexSegment indexSegment, String
columnName, FieldSpec targetFieldSpec) {
+ _segmentColumnReader = new PinotSegmentColumnReader(indexSegment,
columnName);
+ _columnName = columnName;
+ _numDocs = indexSegment.getSegmentMetadata().getTotalDocs();
+ _targetFieldSpec = targetFieldSpec;
+ _currentIndex = 0;
+
+ // Check if data type conversion is needed
+ FieldSpec sourceFieldSpec =
indexSegment.getSegmentMetadata().getSchema().getFieldSpecFor(columnName);
+ _needsConversion = sourceFieldSpec != null
Review Comment:
How about other `RecordTransformer`? Seems the current implementation can
only support `DataTypeTransformer`
##########
pinot-spi/src/main/java/org/apache/pinot/spi/data/readers/ColumnReader.java:
##########
@@ -0,0 +1,83 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.spi.data.readers;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.Serializable;
+import javax.annotation.Nullable;
+
+
+/**
+ * The <code>ColumnReader</code> interface is used to read column data from
various data sources
+ * for columnar segment building. Unlike RecordReader which reads row-by-row,
ColumnReader provides
+ * column-wise access to data, enabling efficient columnar segment creation.
+ *
+ * <p>This interface follows an iterator pattern similar to RecordReader:
+ * <ul>
+ * <li>Sequential iteration over all values in a column using hasNext() and
next()</li>
+ * <li>Null value detection for the current value</li>
+ * <li>Rewind capability to restart iteration</li>
+ * <li>Resource cleanup</li>
+ * </ul>
+ *
+ * <p>Implementations should handle data type conversions, default values for
new columns,
+ * and efficient column-wise data access patterns.
+ */
+public interface ColumnReader extends Closeable, Serializable {
Review Comment:
This is mostly useful when reading from a column major file format such as
Parquet. Can you check if this interface can be used for Parquet reader?
##########
pinot-spi/src/main/java/org/apache/pinot/spi/data/readers/ColumnReader.java:
##########
@@ -0,0 +1,83 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.spi.data.readers;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.Serializable;
+import javax.annotation.Nullable;
+
+
+/**
+ * The <code>ColumnReader</code> interface is used to read column data from
various data sources
+ * for columnar segment building. Unlike RecordReader which reads row-by-row,
ColumnReader provides
+ * column-wise access to data, enabling efficient columnar segment creation.
+ *
+ * <p>This interface follows an iterator pattern similar to RecordReader:
+ * <ul>
+ * <li>Sequential iteration over all values in a column using hasNext() and
next()</li>
+ * <li>Null value detection for the current value</li>
+ * <li>Rewind capability to restart iteration</li>
+ * <li>Resource cleanup</li>
+ * </ul>
+ *
+ * <p>Implementations should handle data type conversions, default values for
new columns,
+ * and efficient column-wise data access patterns.
+ */
+public interface ColumnReader extends Closeable, Serializable {
+
+ /**
+ * Return <code>true</code> if more values remain to be read in this column.
+ * <p>This method should not throw exception. Caller is not responsible for
handling exceptions from this method.
+ */
+ boolean hasNext();
+
+ /**
+ * Get the next value in the column.
+ * <p>This method should be called only if {@link #hasNext()} returns
<code>true</code>. Caller is responsible for
+ * handling exceptions from this method and skip the value if user wants to
continue reading the remaining values.
+ *
+ * @return Next column value, or null if the value is null
+ * @throws IOException If an I/O error occurs while reading
+ */
+ @Nullable
+ Object next() throws IOException;
+
+ /**
+ * Check if the current value (last returned by next()) is null.
+ * <p>This method should be called after {@link #next()} to check if the
returned value represents a null.
+ *
+ * @return true if the current value is null, false otherwise
+ */
+ boolean isNull();
Review Comment:
Why do we need this when `next()` can return `null`?
##########
pinot-spi/src/main/java/org/apache/pinot/spi/data/readers/ColumnReader.java:
##########
@@ -0,0 +1,83 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.spi.data.readers;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.Serializable;
+import javax.annotation.Nullable;
+
+
+/**
+ * The <code>ColumnReader</code> interface is used to read column data from
various data sources
+ * for columnar segment building. Unlike RecordReader which reads row-by-row,
ColumnReader provides
+ * column-wise access to data, enabling efficient columnar segment creation.
+ *
+ * <p>This interface follows an iterator pattern similar to RecordReader:
+ * <ul>
+ * <li>Sequential iteration over all values in a column using hasNext() and
next()</li>
+ * <li>Null value detection for the current value</li>
+ * <li>Rewind capability to restart iteration</li>
+ * <li>Resource cleanup</li>
+ * </ul>
+ *
+ * <p>Implementations should handle data type conversions, default values for
new columns,
+ * and efficient column-wise data access patterns.
+ */
+public interface ColumnReader extends Closeable, Serializable {
+
+ /**
+ * Return <code>true</code> if more values remain to be read in this column.
+ * <p>This method should not throw exception. Caller is not responsible for
handling exceptions from this method.
+ */
+ boolean hasNext();
+
+ /**
+ * Get the next value in the column.
+ * <p>This method should be called only if {@link #hasNext()} returns
<code>true</code>. Caller is responsible for
+ * handling exceptions from this method and skip the value if user wants to
continue reading the remaining values.
+ *
+ * @return Next column value, or null if the value is null
+ * @throws IOException If an I/O error occurs while reading
+ */
+ @Nullable
+ Object next() throws IOException;
Review Comment:
(format) Reformat the changes with [Pinot
Style](https://docs.pinot.apache.org/developers/developers-and-contributors/code-setup#set-up-ide)
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